Sawing cords—sometimes also referred to as sawing wires—are extensively used for sawing stones in quarries and on stationary slabbing machines. Sawing cords are for the purpose of this application understood to be an assembly of sawing beads threaded on a steel cord and spaced apart by a polymer that is injection moulded around the cord.
The sawing bead itself is generally made up of a sleeve to which an abrasive layer is attached. The abrasive layer is made of a compound of metal and abrasive particles that is obtained by powder metallurgy. A mixture of metal powder and abrasive particles are pressed together in an annular shape to form a compact. The compact itself is sintered under a reducing gas atmosphere. The thus densified compact is then brazed onto a small metal sleeve.
Recently an alternative production method has been developed wherein the abrasive layer is directly applied onto the metal sleeve by means of laser cladding. See WO 2012/119946 and WO 2012/119947. Such method can be used in combination with other ways of making a sawing cord as e.g. described in WO 2011/061166.
Although the metal sleeve is only a humble part in the total of a sawing cord, the inventors have found that it does have a large influence on the overall performance of the sawing cord.
As the sleeve is close to the steel cord or even in contact therewith there is the risk for wear of the steel cord. Indeed as the sleeve is relatively rigid compared to the flexible cord the cord may contact the rim of the sleeve upon bending leading to premature failure of the cord. Therefore different chamfered exit openings have been envisioned (see JP10006329, JP9314544, GB 2243094).
Also the bond between the sleeve and the abrasive layer and the bond between the sleeve and the steel cord must be good as all forces acting on the abrasive layer are transferred to the steel cord through mediation of these bonds. To this end it has been suggested to make the sleeves with multiple holes (JP 2000176737) for better anchorage of polymer and abrasive layer.
It has also been suggested to make a recess at the end of the sleeve for better anchorage of the polymer and/or better removal of debris (DE195 22655, EP0728552). DE 195 22655 suggests to make the sleeve in plastic.
As many as 40 beads can be present per meter of sawing cord. So every cent saved results in a decreased cost of 40 cent per meter of wire. At present sleeves are made by machining and cutting from tubes. This is expensive, certainly when one wants to have a controlled and more complicated shape. The inventors therefore explored other ways to produce the metallic sleeve.